1. Field of the Invention
This invention relates to a cylindrical magnetic domain element, and more particularly to a cylindrical magnetic domain element having easily formed and highly efficient propagation patterns for cylindrical magnetic domains (magnetic bubbles).
2. Description of the Prior Art
When a sheet of orthoferrite, garnet or like monocrystalline or amorphous magnetic material having uniaxial magnetic anisotropy, which is grown or sliced in such a manner as to have a magnetic easy axis orthogonal with respect to the plane of the sheet, is exposed to a bias magnetic field orthogonal to the plane of the sheet (in the direction of the magnetic easy axis), a cylindrical magnetic domain (a magnetic bubble) is generated. This magnetic bubble moves according to a magnetic field gradient. This is described in detail in "Domain Behavior in Some Transparent Magnetic Oxides" by R. C. Sherwood, J. P. Remeika and H. J. Williams, Journal of Applied Physics, vol. 30, pages 215 to 225, 1959, and in "Properties and Devices Application of Magnetic Domain in Orthoferrites," Bell System Technical Journal, vol. 46, No. 8, page 1901 to 1925.
By taking advantage of the above said magnetic bubble characteristic (i.e., by detecting the presence or absence of the magnetic bubble in the form of binary information and by combining functions such as magnetic bubble generation, propagation, detection, erasure, division, etc. with one another), it is possible to construct a logic operation unit, a memory, etc. usable in a digital data processing unit.
A variety of conventional magnetic bubble propagation control methods are known. Of the conventional methods, one that has usually been employed is similar to that disclosed in U.S. Pat. Nos. 3,534,347 and 3,543,252. Those patents describe a method of forming propagation patterns of permalloy thin film in various shapes on one or both surfaces of a magnetic sheet and applying a rotating magnetic field parallel with the plane of the magnetic sheet to thereby effect propagation of the magnetic bubble.
Magnetic bubble propagation patterns are generally composed of T-I patterns, Y-I patterns, chevron patterns, or the like, formed of permalloy thin film. The formation of the propagation patterns is usually achieved by either directly depositing permalloy by vacuum evaporation on a magnetic sheet or is deposited on an abnormal magnetic bubble suppressing film, an SiO.sub.2 film, a detecting pattern, a conductor pattern, an SiO.sub.2 film, etc. formed on the magnetic sheet; then coating photoresist on the permalloy; exposing the photoresist to light through a mask having predetermined patterns; developing the patterns; selectively etching away the permalloy to form patterns of the permalloy film; and removing the remaining photoresist.
A propagation pattern formed in the above manner presents the following problems.